A two-dimensional capacitive touch panel includes a plurality of X-traces and a plurality of Y-traces mutually intersected to form a plurality of sensors. When an electrically conductive article such as a finger approaches a sensor, the coupling capacitor between the finger and the sensor will increase the capacitance on the trace connected to the sensor, so a detector circuit can locate the finger on the capacitive touch panel by detecting the capacitance variations of the traces, and then convert the position coordinates into information for a host to perform corresponding operation.
In further detail, as shown in FIG. 1, when a finger touches the intersection point between a Y-trace Y1 and X-traces X4 and X5, the measured capacitances from those X-traces X1, X2, X7 and X8 that are far from the finger will not be affected by the finger and remain below a threshold CTH, the measured capacitances from those X-traces X3 and X6 near the finger will be increased to slightly higher than the threshold CTH, the measured capacitance from the X-trace X5 is even higher, and the measured capacitance from the X-trace X4 where the finger touches is at the peak of the curve 16 established by the measured capacitances from the X-traces X1-X8. Similarly, the measured capacitance from the Y-trace Y1 is at the peak of the curve established by the measured capacitances from the Y-traces, since the Y-trace Y1 is touched by the finger. Therefore, the capacitive touch panel can identify the touch point (X4,Y1). The capacitances on the X-traces X1, X2, X7 and X8 are not affected by the finger, so the measured capacitances therefrom are too low to be useful in the subsequent conversion and calculation for identification of the touch point.
In actual circuitry the capacitance can not be detected directly, and thus a capacitive touch panel performs the capacitance detection by charging its traces one by one and detecting the voltage variations on each of the traces to extract the capacitance variations of the traces. After conversion and processing, the position information is obtained for a host.
The present invention provides a solution for a capacitive touch panel to pre-filter out useless traces and thereby reduce the operation of the detector circuit of the capacitive touch panel. Therefore, the performance of a capacitive touch panel can be improved with higher frame rate and less power consumption.